DOWNHOLE TOOL WITH LIQUID SPRING

A flow tester valve apparatus includes a housing (62) having a flow passage (140) disposed therethrough, with a flow valve (136) disposed therein for opening and closing the flow passage. A power mandrel (148) is disposed in the housing and includes a power piston (156). The power mandrel is operatively associated with the flow valve for moving the flow valve from its closed position to its open position. A power port (192) transmits pressure from a well annulus to a first side of the power piston. A first chamber (242) is disposed in the housing and filled at least partially with a compressible liquid and a second side of the power piston is in fluid communication with the first chamber. A second chamber (258) is disposed in the housing and includes a floating piston (282) which divides the second chamber into a first zone (314) and a second zone (316). An equalizing port (292) is disposed in the housing for transmitting pressure from the well annulus to the second zone of the second chamber. Pressurizing (262) and depressurizing (272) passages communicate the first chamber with the first zone of the second chamber. A first back pressure check valve (268) and a first flow restrictor (270) are disposed in the pressurizing passage. A second back pressure check valve (278) and a second flow restrictor (280) are disposed in the second passage.